Armored Core 2 used the Firewire cable to link up. But the series has switched to LAN play with the network adapter. If you get Nexus, it has two discs and you can use them both to play linked up over a LAN. Also, you can use XLink Kai tunnelling to play online. Nexus also has the option for dual analog control, which fucking rocks, not to mention some other kick ass features.